Wi-Fi® equipment and Licensed-Assisted Access (LAA) of the Long Term Evolution (LTE) wireless standard are expected to share the same spectrum (5 GHz for example). To ensure fair co-existence in the same channel, LAA-LTE is expected to deploy some form of Listen-Before-Talk (LBT) and back-off mechanisms. Due to differences in defer and back-off mechanisms between LAA-LTE and Wi-Fi, there are challenges in defining a single unified rule in maintaining a fair co-existence without careful selection of fairness parameters.
Some LBT mechanisms may be required in certain regulatory domains (like the European Telecommunications Standards Institute (ETSI), for instance). The sensing mechanism required is “energy-detect” in the operating channel. For example, Wi-Fi implements Clear Channel Assessment Energy Detect (CCA-ED) to detect non Wi-Fi sources in the operating channel. This threshold typically set to −62 dBm/20 MHz.
Third Generation Partnership Project (3GPP) Release-13 LAA-LTE defines something similar to CCA-ED. However, in many deployment scenarios this will not be enough to avoid collisions between Wi-Fi and LAA-LTE. A Wi-Fi device and LTE device implementing LAA may not be able to detect each other based on energy detect thresholds, but a Wi-Fi receiver may indeed be interfered with by a LAA-LTE transmitter and vice versa. Specifically, if a Wi-Fi device and an LAA-LTE device were to transmit at the same time, there will be incidents of packet collisions. This is more likely to happen between Wi-Fi and LAA-LTE devices than between two different Wi-Fi devices because preamble detection will likely only be implemented between two Wi-Fi devices.
Additionally, LAA-LTE subframes in the unlicensed band, e.g., the shared spectrum, are likely to be aligned with the subframes in the licensed band. Further, the wireless transmission in the shared spectrum is likely to be forced to begin at the start of an LTE subframe. However, an idle medium may occur at any part of a subframe, and a requirement to begin the LAA-LTE transmission only at the beginning of the LTE subframe may cause the medium to remain idle for longer than necessary, wasting resources.